For Earth Day 2013, on Monday, April 22nd, we are offering an 85% discount on all E-books on our site.
How to claim your savings: After you've added all the pdf E-books you want to your cart, proceed to checkout and enter the code "EARTH13" in the discount code box. Once you hit the "Continue" key, but before you enter your credit card information, the price on the E-books will be changed to reflect the discount. The price on print books will not change.
This picture below highlights where exactly on the checkout screen you enter your special EARTH13 code.